The present invention relates to a recording sheet used for a inkjet printing method, and relates in particular to an inkjet recording sheet improved so that blurring of recorded images does not occur.
Inkjet printers have characteristics such as clarity of the produced images, silent operation, ease of coloring, and the like; therefore, they are one of the most popular printing devices at the present time. In order to prevent the nozzle from with filing dried ink, ink which is difficult to dry has been used in inkjet printers. The ink which is difficult to dry in general comprises coloring agents such as pigments, and dyes; solvents such as aqueous solvents, and water-soluble solvents; additives; and the like. In particular, absorption with aqueous materials or water-soluble materials is needed for a recording sheet used in inkjet printing methods. Therefore, the recording sheet popularly comprises an ink absorbing layer on a substrate.
The ink absorbing layer comprises a mixture as a main component in which pigments, such as silica, having high water absorbing properties are mixed into water-soluble polymers such as polyvinyl alcohol; other water-soluble polymers; and additives. However, conventional recording sheets having the above compositions have problems such as ink absorbing properties being insufficient and dry properties (fixing properties) of the ink being poor.
In order to solve these problems, improving the water absorbing properties of the recording sheet by adding a large amount of pigment having high water absorbing properties such as silica to the ink absorbing layer. However, not only is the ink absorbing layer not suitable for practical use because blurring of the printed images during printing is large, but it has poor storing properties, namely blocking occurs between adjacent sheets during storage because the surface of the ink absorbing layer becomes sticky due to the absorption of moisture. In particular, recent inkjet printers tends to be used for the purpose of making full color prints, and the amount of ink used in printing to bring out the colors is large. The problem is serious.
Moreover, in order to overcome the problem of the blurring of printed images, a recording medium in which an ink absorbing layer comprises hydrophobic materials such as salt of fatty acid is suggested in Japanese Patent Application, First Application No. 62-204990. However, hydrophobic materials must be dispersed in hydrophilic resin in this method; therefore, it is difficult to provide an ink absorbing layer having uniform components. Blurring of the printed images can be slightly reduced by the ink absorbing layer. However, the ink absorbing layer has some problems in obtaining a uniform full color image.